As shown in FIG. 1, a prior art mop 10 has a colloidal cotton 12. In operation, a pull rod 14 is pulled to actuate the colloidal cotton 12 to move upwards by two connection rods 15 such that the colloidal cotton 12 is held between the two press bars 1 of a pressing mechanism 16, as shown in FIG. 2. The colloidal cotton 12 is thus squeezed dry to be ready for cleaning the floor. As the colloidal cotton 12 picks up dirt on the floor, the colloidal cotton 12 is washed with head to remove therefrom dirt. The soaked colloidal cotton 12 is once again squeezed dry by the pressing mechanism 16 so as to be ready for cleaning the floor.
The prior art mop 10 has shortcomings. For example, the colloidal cotton 12 has a bottom edge, which is kept under the two press bars 17 at the time when the colloidal cotton 12 is actuated to move upward to locate at a dead point. This is to present the colloidal cotton 12 from being retracted into a head 11 of the mop 10, as illustrated by the solid lines in FIG. 2. If the bottom edge of the colloidal cotton is aligned with the press bars 17, the colloidal cotton located over the press bars is likely retracted into the head to separate from the press bars, as shown by the imaginary lines in FIG. 2. In view of the fact that the bottom edge of the colloidal cotton can not be squeezed, the colloidal cotton can not be squeezed dry in its entirety. As a result, the excessively wet colloidal cotton can not clean the floor effectively. In addition, the floor becomes wet and slippery. Moreover, after a prolonged use of the mop 10, the colloidal cotton is prone to shrink to be retracted into the head. The retraction of the colloidal cotton into the head may be also resulted from the fact that the colloidal cotton is connected by the pull rod 14 and the connection rods 15, and that the upper dead point of the colloidal cotton is prone to be dislocated. When the colloidal cotton is retracted into the head such that the colloidal cotton becomes separated from the press bars, the prior art mop 10 can not be used again due to the fact that the colloidal cotton can not be actuated to move by the pull rod.